The present invention relates to tungsten carbide hardfacing compositions and products produced therefrom. It especially relates to those hardfacing compositions which contain monocrystalline monotungsten carbide particles, hereinafter referred to as macrocrystalline WC.
Many tungsten carbide hardfacing compositions and methods for applying these compositions are known in the art. Examples of these compositions and methods are described in U.S. Pat. Nos. 3,768,984; 4,243,727; 3,800,891; 3,334,975; and 3,329,487. Hardfacing compositions have been applied to components used in earth drilling equipment to prolong the lifetime of these components by increasing their wear resistance. For example, the teeth of multiple cone roller bits have been rebuilt using hardfacing retipping rod.
One type of retipping rod utilized contained a blend of -40 +100 mesh eutectic W.sub.2 C-WC, AISI 4600 steel powder, iron powder, carbon binder in the form of sugar, 0.9 to 1.32 weight percent -325 mesh niobium metal powder, and 2.07 to 4.14 weight percent -100 mesh molybdenum metal powder. This blend of hardfacing powder was contained within a hollow mild steel rod which was consumably melted onto the multiple cone teeth to be rebuilt.
Also, in the field of earth drilling, it has been observed that bulk hardfaced drill pipe couplings with a larger diameter than the drill pipe have a tendency to abrade and damage the drill casing, especially during deep well drilling. The abrasion of the casing has been related to the fact that the tungsten carbide particles in the hardfacing protrude above the steel matrix of the weld pool. One attempt to provide improved submergence of the tungsten carbide particles in the weld pool (see U.S. Pat. No. 4,243,727) involved dropping cemented tungsten carbide granules directly into the weld puddle at the arc, rather than at a point following the arc, as had been the practice. The higher temperatures found in the weld puddle at the arc, however, result in greater dissolution of the tungsten carbide into the steel matrix and can lead to a reduction in the toughness of the steel matrix.
Drill couplings have also been bulk hardfaced by dropping macrocrystalline WC into the weld pool. While drill couplings hardfaced in this manner are usable, they have significant amounts of macrocrystalline WC protruding above the weld pool and exhibit a significant number of cracks at the weld deposit surface.
It is, therefore, an object of the present invention to provide hardfacing powder mixtures which can be applied to wear surfaces using conventional hardfacing techniques and result in submergence of substantially all of the tungsten carbide particles in the weld pool.
It is also an object of the present invention to provide a hardfacing powder mixture utilizing macrocrystalline WC.
It is a further object of this invention to provide hardfaced wear products containing macrocrystalline WC and which are substantially free from surface cracks.
These and other objectives of the present invention will become more clearly apparent upon review of the following specification in conjunction with the attached drawings.